Sustainable Design for Production of Styrene from Benzene and

Ethylene

Kasper Hartvig Lejre, Kasper Fjellerup, Magnus Zingler Stummann, Marina Fedorova*

Computer Aided Process Engineering Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DK-2800 Lyngby, Denmark

*mfad@kt.dtu.dk

The usage of styrene monomer has been increasing for several decades, and there is no sign of the consumption slowing down. Therefore increased production facilities are needed to satisfy the demand. Styrene monomer is used for the production of a large range of polymers and co-polymers; these include polystyrene, latex and rubber.
There are several pathways to form styrene, but this project, which was done in an MSc Process Design course conducted at DTU, proposes to design a plant to produce styrene through two major reaction steps. The first step is high-pressure alkylation of ethylene and benzene to ethylbenzene and the second step is dehydrogenation of ethylbenzene to form styrene.
The production process is designed systematically using the hierarchical decomposition approach for process synthesis, where the synthesis-design problem is decomposed into
12 hierarchical tasks. According to the design, the process will produce on a yearly basis around 168,000 metric tonne of styrene with a yield of 0.87 kg product per kilo of raw material.
Heat integration and process optimization are performed on the base case design, significantly decreasing the energy consumption for the process, where mainly the compression work and reboiler duties need a majority of the energy. A decanter is installed to remove a major part of the water after the dehydrogenation reaction, which results in a decrease of distillation column sizes, which lowers the reboiler duty by 25 % and the condenser duty by 37 %. After heat integration the external utilities are reduced by 85 %.
Finally, a sustainability and environmental impact analysis is performed based on software tools: LCSoft and SustainPro. A more sustainable design is obtained by addressing the identified process bottlenecks.